Process for drawing polypropylene yarn



Jan. 31, 1967 J. c. WEBNAR 3,301,934

PROCESS FOR DRAWING POLYPROPYLENE YARN Filed June 18, 1963 3 SheetsSheet 1 J. C. WEBNAR L IN\ENT()R.

Jan. 31, 1967 J. c. WEBNAR 3,301,934

PROCESS FOR DRAWING POLYPROPYLENE YARN 3 Sheets-Sheet 2 Filed June 18, .1963

J. C. WE AR INVE )R.

BY "1 LLJQJ Ki U AGENT Jan. 31, 19.67 J. c. WEBNAR 3,301,934

PROCESS FOR DRAWING POLYPROPYLENE YARN Filed June 18, 1963 5 sneets sneet a J. C. WEBNAR INVENTOR.

United s, Petentt) 3,301,934 PROCESS FOR DRAWING POLYPROPYLENE YARN Joseph C. Webnar, Roanoke, Va., assignor to Hercules Incorporated, a corporation of Delaware Filed June 18, 1963, Ser. No. 288,668 3 Claims. (Cl. 264-290) characterized by high tensile strength, great durability,

rot and fungus resistance, and low density. 7

In the usual procedures for formation of textile fibers from synthetic organic materials, molten polymer is pumped through a multi-orifice spinneret, subjected to a draw down in the melt, and contacted with cooling air to quench and solidify the polymer. The plurality of individual filaments are combined into a single thread or yarn and are wound onto a spool or bobbin. In a further ope-ration, the yarn is stretched to impart molecular orientation and to enhance its physical properties.

The conditions employed in the stretching operation vary somewhat depending upon the properties of the polymer being drawn but, in order to produce filaments of uniform denier, it is usually necessary that the stretching be done at an at least slightly elevated temperature and that it be confined to a relatively small area. To this end, the usual stretching process for polypropylene yarn comprises feeding the yarn over a heated positively driven feed roll to a heated draw roll which is positively driven at a greater peripheral speed than the feed roll.

In order to effect the correct amount of heat transfer to the filament as it passes around the heated feed roll it is frequently, if not always, necessary that the filament be wrapped around the feed roll several turns. In order for 3,301,934 Patented Jan. 31, 1967 experimentation it has been found that chalkiness in polypropylene yarn that has been stretched by the above referred to equipment is related to the manner in which heat is applied to the yarn as it is brought to optimum temperature for stretching. More specifically, chalkiness has been found to be related to the uneven rise in the temperature of the yarn as it passes around the idler roll and through the air spaces between the idler roll and the feed roll. The uneven rise in the temperature of the yarn results in certain physical effects within the individual polymer particles that are as yet unexplained.

These physical effects manifest themselves as chalkiness when the yarn is stretched.

Briefly, the present invention resides in minimizing the uneven rise in the temperature of the yarn by reducing or preferably substantially eliminating the temperature differential to which the yarn is exposed in the above referred to stretching equipment as it passes from the feed roll to the idler roll, around the idler roll, and back to the feed roll. To minimize the temperature differential,

, heat is supplied to the yarn substantially continuously,

that is, not only as it passes around the feed roll, but also as it passes to, around, and from the idle-r roll. In this manner, chalkiness in the stretched yarn is prevented while the yarn can be drawn at lower temperatures. for increased strength.

A preferred embodiment of the invention together with modifications thereof are hereinafter described in connection with the accompanying drawings.

In the attached drawings, FIG. 1 is a cross-sectional I view of a preferred embodiment of the invention, using heat transfer from the roll to the filament to be most efficient, the individual wraps must be kept separated on the roll. This is usually accomplished by associating with each feed roll, at a distance of a fraction of an inch to several inches therefrom, an idle-r roll, canted at a slight angle to the axis of the feed roll. The filament passes around the feed roll and its associated idler roll as a unit, the cant of the idler roll being sufficient to cause the filament wraps on the feed roll to separate and remain separated so that each wrap is in contact with the heated surface of the feed roll.

Although the process just described has been found to be quite satisfactory when applied to other synthetic filament forming materials, it'has not been overly successful with polypropylene. When polypropylene yarn is drawn using this equipment, it shows a tendency to assume'a milk white, chalky, opaque appearance beneath its surface unless stretching conditions are extremely precisely controlled. Such yarn, referred to as chalky yarn, is not commercially desirable and the greater portion of it usually must be scrapped, resulting in decreased yields and concurrently higher costs. It is known that, in polypropylene yarn to be stretched by the above drawing method that includes the use of a heated feed roll, chalkiness can be eliminated or reduced by running the temperature of the feed roll very high. However, maintaining yarn at the high temperatures required is undesirable because such temperatures impose limitations on the maximum draw that can be performed on the yarn and results in yarn having reduced tensile strength.

In accordance with this invention, through considerable heated platens. FIGS. 2 and 3 are perspective views of alternative embodiments of the heated platen concept. FIG. 4 isa cross-sectional view of the embodiment of the invention wherein the feed roll and idler assembly are housed within a heated enclosure.

In FIG. 1, the equipment used in the process comprises a positively driven yarn feed roll 3, an idler roll 4 associated therewith, heated platens 5 located intermediate the feed and idler roll, and a draw roll 6 with its associated idler roll 7. The embodiment depicted in FIG. 2 comprises a feed roll 9, a single heated platen 10, and an idler roll 11. The idler roll and heated platen are assembled into a single unit 12.

The equipment arrangement depicted in FIG. 3 comprises a feed roll 13 and a single heated platen 14.

In FIG. 4, the feed roll 15 and idler roll 16 are housed within an enclosure 17. Radiant heaters 18 provide heat within the enclosure.

The operation of the process of the invention will be explained in relation to the attached FIG. 1.

In stretching of polypropylene yarn according to the invention, undrawn yarn 1 is unwound from a bobbin 2 over a feed roll 3, heated to a temperature between about and C., and its associated idler roll 4, also heated to the same temperature. In the gap intermediate the feed roll and the idler, which usually is a distance of about /2 to 6 inches, the yarn maintains contact with the heated metal platens 5, also maintained at a temperature of 80 to 135 C. The yarn may describe any desired number of wraps around the feed roll/ idler combination, the number being determined only by the degree of heat transfer required, usually being between 4 and 20 wraps.

The platens may be constructed of any suitably smooth, highly heat conductive material. Stainless steel is an eminently suitable material fitting this description. Heat can be supplied to the feed and idler roll and to the intermediate platens by any convenient heat transfer technique. Such techniques include circulation of a heated liquid such as steam and electrical heating.

Though the choice of heating means and construction materials is not critical, it is desirable that all of the heated members be heated by the same means, con- 7 struoted of the same material, and all be subject to the same control since precise temperature control of the yarn in traveling over the unit is one of the objectives of the invention.

From the feed roll the yarn is fed around the draw roll 6, driven about 1.75 to 10 times the speed of the feed roll in order to draw the heated yarn and enhance its typical properties. Upon cooling to room temperature, the yarn is rewound on bobbin 8.

In the following examples, the yarn was drawn using the embodiment of the invention shown in FIG. 1.

Example 1 Undrawn, twisted polypropylene yarn spun 630/105 was drawn using the feed roll/idler roll system with and without the heated platens. The feed roll was 8 inches in diameter, its idler roll 3%; inches in diameter canted at a 2 angle, and removed from the feed roll by a distance of 2 /2 inches at the maximum point. The following conditions were used with each system:

(a) Feed roll temperature, 135 C.

(b) Feed roll wraps, 8.

(c) Drawing speed, 250 meters per minute.

((1) Draw ratio, 3.

Quality-wise, yarn is classified as:

' (a) First quality-perfect yarn, bright, lustrous and translucent, chalkiness completely absent.

(b) Second qualitysome chalkiness is apparent, but yarn is commercially acceptable in some limited applications.

Off quality-completely chalky, milk white in appearance, commercially unacceptable.

The yarn produced in Example 1 using the standard system without the heated platens was second quality; that produced using the platens was first quality.

Example 2 Undrawn, twisted 630/140 polypropylene yarn was drawn using the feed roll/idler roll system of FIG. 1 with and without the heated platens. The feed roll was 8.5 inches in diameter its idler roll 3 /8 inches in diameter canted at a 2 angle, and separated from the feed roll by a distance of 2 /2 inches at the maximum point. The following conditions were used with each system:

(a) Feed roll temperature, 80 C.

(b) Feed roll wraps, 8.

(c) Drawing speed, 180 meters per minute. 1) Draw ratio, 4.7.

The yarn produced in this example using the heated platens of this invention, was first quality, whereas the yarn produced without the platens was off quality.

In the embodiment of the invention shown in FIG. 2 the principle of operation is identical to that shown in FIG. 1, the only difference being that the heated platens '9 and the idler roll 10 are constructed and installed as a single unit. The platens are tapered at the necessary angle to give the rotating idler the correct amount of cant.

' roll causes the yarn to travel.

The term idler roll is not limited in this specification to its strict sense of a rotatable roll but in a broad sense to indicate a generally hemispherical surface, rotatable or not, which serves the function of causing the yarn to travel along the surface of its associated feed roll and prevent overlapping of wraps.

FIG. 3 shows an embodiment of the invention wherein the heated platen 14 is a non-rotatable, hemispherical, heated surface over which the yarn travels in continuous sliding contact to prevent loss of heat. The surface is so tapered as to cause the yarn to travel along the feed roll surface in the same manner that canting of the rotatable Thus, element 14 serves both the function of a separator, or idler, roll and the function of heating means for the yarn in its travel.

The apparatus of FIGS. 2, 3, and 4 can be used in place of the apparatus of FIG. 1 with equivalent results.

What I claim and desire to protect by Letters Patent is:

1. In the process for drawing polypropylene yarn wherein a plurality of turns of yarn are wrapped about a driven feed roll and about an idler roll disposed in spaced relation to the feed roll and arranged at a small angle out of parallel to said feed roll whereby said turns of yarn are guided along said feed roll without overlapping, wherein said yarn is also wrapped about a draw roll disposed in spaced parallel relation to said feed roll and driven at a speed greater than that of said feed roll whereby the yarn is drawn between said feed roll and said draw roll, and wherein said yarn is heated at said feed roll to a desired temperature for drawing, the improvement comprising, in said heating, continuously supplying heat to said yarn at a substantially uniform temperature as said yarn passes around said feed roll and said idler roll and between said ifeed roll and idler roll for raising the temperature of said yarn uniformly whereby the yarn is adapted to be drawn at relatively low temperatures and without chalkiness.

2. In the process for drawing polypropylene yarn in accordance with claim 1 wherein said heating is supplied by heating said feed roll and said idler roll, and by a heated platen between said feed and idler rolls along which yarn slides.

3. In the process for drawing polypropylene yarn in accordance with claim 1 wherein said heating is supplied by enclosing said feed roll and idler roll within a heated enclosure.

References Cited by the Examiner UNITED STATES PATENTS 2,617,007 11/1952 Atkins 264290 2,956,330 10/1960 Pitzl 264-290 3,083,412 4/ 1963 Brignac et al. 264-290 3,101,990 8/1963 Heighton 264290 3,229,015 1/1966 Kramer 264-290 FOREIGN PATENTS 1,309,857 10/1962 France.

ALEXANDER H. BRODMERKEL, Primary Examiner.

B. SNYDER, Assistant Examiner. 

1. IN THE PROCESS FOR DRAWING POLYPROPYLENE YARN WHEREIN A PLURALITY OF TURNS OF YARN ARE WRAPPED ABOUT A DRIVEN FEED ROLL AND ABOUT AN IDLER ROLL DISPOSED IN SPACED RELATION TO THE FEED ROLL AND ARRANGED AT A SMALL ANGLE OUT OF PARALLEL TO SAID FEED WHEREBY SAID TURNS OF YARN ARE GUIDED ALONG SAID FEED ROLL WITHOUT OVERLAPPING, WHEREIN SAID YARN IS ALSO WRAPPED ABOUT A DRAW ROLL DISPOSED IN SPACED PARALLEL RELATION TO SAID FEED ROLL AND DRIVEN AT A SPEED GREATER THAN THAT OF SAID FEED ROLL WHEREBY THE YARN IS DRAWN BETWEEN SAID FEED ROLL AND 